Creating these flavorful Stuffed Spinach Mushrooms is easier than you might think! Follow these detailed, step-by-step instructions to guide you through the process, from prepping the mushrooms to baking them to golden perfection:

1. Preheat Oven and Prepare Mushrooms: Preheat your oven to 375°F (190°C). This temperature ensures the mushrooms cook through and the stuffing becomes golden brown without burning. While the oven is preheating, prepare the mushrooms. Gently wash the mushrooms under cool water to remove any dirt. Avoid soaking them, as they can absorb water. Pat them dry thoroughly with paper towels. Remove the stems from each mushroom cap by gently twisting and pulling them out. Set the mushroom caps aside and finely chop the stems. Don’t discard the stems – they add wonderful flavor to the stuffing!
2. Sauté Aromatics and Mushroom Stems: Heat 2 tablespoons of olive oil in a large skillet over medium heat. Once the oil is shimmering, add the minced shallot and chopped mushroom stems to the skillet. Sauté for about 3-5 minutes, or until the shallots are softened and fragrant and the mushroom stems have released some of their moisture and slightly browned. Add the minced garlic to the skillet and sauté for another minute until fragrant, being careful not to burn the garlic. Burnt garlic can become bitter.
3. Wilt Spinach: Add the fresh spinach to the skillet. You may need to add it in batches as it wilts down quickly. Cook, stirring occasionally, until the spinach is completely wilted and tender, usually about 2-3 minutes. Once wilted, remove the skillet from the heat.
4. Drain Excess Moisture (Important Step!): This is a crucial step to prevent soggy stuffed mushrooms. Transfer the spinach mixture to a fine-mesh sieve or colander set over a bowl. Press down on the spinach mixture with the back of a spoon or spatula to squeeze out as much excess moisture as possible. Discard the liquid or reserve it for adding to soups or sauces later. Removing the excess moisture is key to a perfectly textured stuffing.
5. Prepare the Stuffing Mixture: In a medium bowl, combine the softened cream cheese, grated Parmesan cheese, panko bread crumbs, dried Italian seasoning, and red pepper flakes (if using). Add the drained spinach and mushroom mixture to the bowl. Season generously with salt and freshly ground black pepper. Mix everything together thoroughly with a spoon or spatula until all ingredients are well combined and the stuffing is cohesive. Taste the mixture and adjust seasoning as needed.
6. Stuff the Mushroom Caps: Lightly drizzle the mushroom caps with olive oil, both inside and out. This helps prevent them from drying out during baking and adds flavor. Using a small spoon or your fingers, generously fill each mushroom cap with the spinach and cheese stuffing. Mound the stuffing slightly on top of each cap.
7. Bake the Stuffed Mushrooms: Arrange the stuffed mushroom caps in a single layer on a baking sheet. You can line the baking sheet with parchment paper for easier cleanup, although it’s not strictly necessary. Sprinkle the tops of the stuffed mushrooms with additional grated Parmesan cheese for a golden, cheesy crust. Bake in the preheated oven for 20-25 minutes, or until the mushrooms are tender and the stuffing is golden brown and heated through. The cooking time may vary slightly depending on the size of your mushrooms and your oven.
8. Rest and Garnish (Optional): Once baked, remove the baking sheet from the oven and let the stuffed mushrooms rest for a few minutes before serving. This allows them to cool slightly and the flavors to meld together. Garnish with fresh chopped parsley, if desired, for a pop of color and freshness.
9. Serve Warm and Enjoy!: Serve the Stuffed Spinach Mushrooms warm as an appetizer or side dish. They are best enjoyed immediately while they are still warm and cheesy.

Following these detailed instructions will ensure you create perfectly cooked, flavorful, and satisfying Stuffed Spinach Mushrooms that are sure to impress your guests or simply elevate your meal. Enjoy!